Start with a database constraint that cost me 200 customers over 1 year. Yahoo users couldn't sign up. I didn't know. They never became customers.
My British IPTV business was growing. Traffic was up. Advertising was working. But signups from Yahoo email addresses were suspiciously low. I assumed Yahoo users weren't interested. I was wrong. They were interested. They were blocked. A database constraint had a bug. It rejected any email with a hyphen. Yahoo allows hyphens. My database didn't.
Here's the thing — email constraints are invisible. Your British IPTV business loses customers. You never know why.
What actually works is monitoring signup completion rates by email domain. Yahoo. Gmail. Outlook. iCloud. If one domain has significantly lower completion rates, investigate.
One real-world scenario: a reseller in Manchester ran a domain completion report. He found that Yahoo signups had a 40% lower completion rate. He investigated. He found a hyphen constraint. He fixed it. Yahoo signups doubled.
The pattern that keeps showing up is that email constraints are invisible. Your British IPTV business needs domain monitoring.
The 2 AM database constraint taught me to monitor signups by email domain. Yahoo matters.
A loose sentence: A database constraint that blocks Yahoo is a constraint that blocks loyal users. Test your signups with every email domain.